Godzilla king of the monsters Ghidorah questions?

First, why would Ghidorah essentially waste the time and effort to kill humans that couldn’t possibly be of any threat? I don’t mean pilots/soldiers and such. Specifically those who have no weapons and are just running on foot. Also don’t mean any that are killed by being crushed unintentionally.

Second, Godzilla clearly is quite intelligent and can determine the best way to fight in different situations or environments. Why not either attack or lure Ghidorah to an ocean, and drag him or pull him under water. It’s not mention if he could survive under water exactly, although it could be since the oxygen destroyer didn’t work. If we do assume he can’t, Godzilla could easily drown him since he is able to breathe under water for a long time, if not indefinitely.